US 2012/0286574 A1 discloses an electric power system with a first unit equipped with a first power source, a first rechargeable battery connected to an output of the first power source and a first power consuming portion connected to an output of the first rechargeable battery. The electric power system further comprises a second rechargeable battery and an electrical power line for sharing electric power between the first rechargeable battery and the second rechargeable battery.
US 2007/0029879 A1 discloses a DC power distribution system comprising a DC power converter configured to provide DC power to at least one DC powered electronic device and at least one DC conductor set for coupling the DC power converter to at least one DC outlet, wherein the DC outlet is adapted to connect the at least one DC powered electronic device to the DC power distribution system.
U.S. Pat. No. 7,923,857 B2 discloses a system for supplying power to a plurality of actuators on board of an aircraft. The system comprises a plurality of generators to supply alternating current and a plurality of conventional electrical master boxes configured to supply power to power loads, wherein the plurality of conventional electrical master boxes has a plurality of power transfer units and is positioned at a first and second side of the aircraft. The power loads include air conditioning units, units to protect against icing and engine starters. The system further comprises two devoted master boxes configured to each receive power from a least one conventional master box via the plurality of power transfer units and to supply the power only to actuator loads, wherein the two devoted master boxes are connected to the plurality of conventional electrical master boxes at the first and second side of the aircraft and wherein the actuator loads include flight control and wheel brakes.
DE 197 57 113 A1 discloses a coupling network for supplying DC power from a DC power network to a consumer, wherein the coupling network comprises a circuit unit for switching the power supply on and off. The power supply comprises at its input side two separate subnetworks, which at the output side are connected with electrical consumers via electrically actuatable switches such that each subnetwork contributes to the supply of the electrical consumers at the output side depending on the respective capability.
Power-over-Ethernet (PoE) is a standard to supply power to detached data equipment and peripherals (like routers, switches, printer spoolers etc.) through the same wire or network connection that is already used to connect these to the Ethernet. Currently discussions are coming up to (mis)use the same standard for all kinds of low power loads like lighting equipment (sensors, switches, light sources etc.) or entertainment appliances like active speakers, internet radios, DVD player, set-top boxes and even TV sets. Here, actual standardization in IEEE802.3 is going on to support power levels even up to 60 W per Cat5/6 connection.
One upcoming field for applying PoE is in lighting systems. The new generation of LED based lamps make use of a central power supply as provided by PoE in the network infrastructure. In addition the use of cheap network cables reduces installation costs and inherent safety (due to low DC power) and polarity independence reduce installation errors which, if they occur during installation, can be identified immediately because power does not need to be shut off like required in conventional lighting installations connected to mains directly. Most load devices are light sources. However, other devices like sensors or user interface devices (switches, control panels) may also be powered by PoE.
As PoE supply systems for power distribution inside of buildings get into the view of the industry, specific drawbacks of these networks need to find solutions in order to get these direct current powered networks (so called “DC-Grids”) widely employed. When the PoE standard was introduced for supplying power to detached networking devices like routers, switches, printer spoolers, etc., it was a replacement for small power-plug type power supplies, since the originally intended loads where mostly already equipped with communication and processing means.
FIG. 1 shows a typical connection of a conventional PoE system comprising a power sourcing equipment (PSE) 1 and one PoE load 20 usually called powered device (PD). A connection may be implemented by means of a so called patch cable 14 between one of a plurality of output jacks or ports 12 of the PSE 1 and an input jack or port 21 of the PD 20. In PoE systems, typically power supplies 11, 24 and data connectivity of a data processing functions 19, 25 are sharing the same patch cable 14. In multi load systems, each load gets connected by a PSE manager 18 to a separate one of the plurality of output ports consisting of first port (P1) 12 to an n-th port (Pn) 13 of the PSE 1. So each load, such as the PD 2, negotiates separately the availability of required power with the PSE 1. This requires a powered device controller 23 in each load (i.e. PD 20). On the PSE side a PSE management controller 18 supervises the negotiations on all ports.
However, in the new application field of lighting systems or similar load systems with often small loads with low local computing and communication requirements, sometimes the overhead of communication and processing compared to the load complexity is inappropriate. Moreover, another shortcoming of PoE is its purely star-based network topology, while lighting systems are often wired in a serial manner (i.e. daisy-chained). Due to this, implementation of the star-based PoE in these kinds of typically serially connected load systems would lead to increased total cable lengths and thick cable bundles in comparison with a truly serially connected implementation. In cases where light systems connected to PoE are equipped with local storage and lights do not need to be switched on continuously like in many cases, the load over the serially connected cables can be divided in time resulting in a far more limited current in the cable which is closest to the PoE switch.